In each graph the log of molar concentration of test compound is plotted against the effect of the compound on the hERG current, expressed as a percentage of the pre-compound signal. In this experiment an average of 9±3% signal decay was observed in the time- and vehicle (DMSO) control. Data are normalised for this vehicle-response such that a value of 100% = no drug effect. The smaller grey symbols represent data from individual cells. The larger blue points show the mean data at each test concentration. The line of best fit (4 parameter logistic equation) is generated from the individual cell data points. Outlier data points (boxed symbols) were manually excluded from the curve fit. No more than two per curve were excluded, other than where compounds were visibly out of solution.

Details of methodElectrophysiological recordings were made from a Chinese Hamster Lung cell line stably expressing the full length hERG channel. Single cell ionic currents were measured in the perforated patch clamp configuration (100 μg ml-1) amphoterocin) at room temperature (21-230C) using an IonWorks Quattro instrument. The internal solution contained (mM): 140 KCl, 1 MgCl2, 1 EGTA, 20 HEPES and was buffered to pH 7.3. The external solution contained (mM): 138 NaCl, 2.7 KCl, 0.9 CaCl2, 0.5 MgCl2, 8 Na2HPO4, 1.5 KH2PO4 also buffered to pH7.3. Cells were clamped at a holding potential of -70mV for 30s and then stepped to +40mV for 1s. This was followed by a hyperpolarising step of 1s to -30mV to evoke the hERG tail current. This sequence was repeated 5 times at a frequency of 0.25Hz. Currents were measured from the tail step at the 5th pulse, and referenced to the holding current. Compounds were then incubated for 6-7 minutes prior to a second measurement of the hERG signal using an identical pulse train.

Electric cycle method

The following QC conditions were applied:

(1) Individual cells with any of the following properties were excluded from subsequent analysis: (1) seal resistances <50MOhms (2) hERG currents <150pA (3) seal resistances that changed by >50% during the experiment